In the past, pressurized fluid supplied to working means such as hydraulic and pneumatic cylinders has generally been controlled by special complex valves known as "spool valves". Such spool valves incorporate a linear shifting spool which alternately connect selected multiple fluid flow passages together. Such spool valves incorporate a linearly shifting spool fitted inside a cylinder. The spool has multiple flow grooves cut in its surface at various locations and the cylinder has internal cylindrical grooves under cut within its surface separated by sealing O-rings such that linear motion of the spool aligns the flow grooves for passage of fluid from one of the cylindrical under cut grooves to another one of the cylindrical under cut grooves. Selection of which under cut grooves are to be inter-connected is determined by moving the spool linearly from one position to another.
The spool valves require special machining inside the bore to create the multiple under cut grooves into which the seals are inserted and those inter-connected with the various fluid flow passages. This special internal machining of the cylinders requires high initial cost. Not only is the process time consuming; but, there is a high degree of material rejection due to metal porosity. Leaks around the type of required deep groove cuts are not acceptable for proper spool valve operation. Also spool valves present high cost to the user because maintenance is complicated when the internal seals require replacement. Seal wear is accelerated because of the nature of a spool having grooves in its external surface sliding back and forth over the seals and also because the pressurized fluid is in direct contact with the rubberized or flexible seals as it flows past from one selected passage way to a second selected passage way to be inter-connected.
The fluid flow characteristics of the spool valve is often adversely affected by its high internal restriction of fluid flow. The convoluted flow path of the fluid through the spool valve can slow reaction time and reduce the net effective pressure or power to the working cylinders.
Heretofore pressurized fluid flow control with individual valves have been used primarily to interrupt single direction fluid flow streams or have been utilized to select between two pressurized fluids sources joined with a single fluid outlet. These prior valve assemblies such as of the poppet type have generally had poppets which are directly actuated by rotary cam plates or lever arms. For example, U.S. Pat. No. 2,441,253 describes a valve assembly having a number of radially oriented poppet valves selectively actuated by contact with the exterior surface of a rotary cam. The poppet valves are arranged perpendicular to the axis of rotation of the cam and is designed for inter-connecting one of the several radially oriented passage ways with a single axial passage way. Because of the direct actuation of the poppet valves, considerable external force must be applied to rotate the cams.
Other poppet valves are described in U.S. Pat. No. 2,580,731 and in U.S. Pat. No. 3,756,284; both of which show a toggle lever actuated valve arrangement such that the user chooses between opening one of two poppet valves depending on the direction the toggle lever is moved. Again, as direct actuation is required considerable external force must be applied to move the lever arms. Moreover, neither of these prior patents show or suggest a valve assembly adaptable for controlling fluid pressure to a pressure actuated working means such as a push and pull hydraulic piston and cylinder device where pressurized fluid must simultaneously flow to and from the working means.
Another valve assembly is disclosed in U.S. Pat. No. 2,609,207 which employs a handle that is rotated to a plurality of index positions and then pivoted for depression against a spring force to actuate a selected valved arrangement. This valve assembly is adapted to be connected between a source of fluid pressure and one or a plurality of fluid pressure actuated motors such as double acting or reversible oscillating or reciprocating piston or cylinder devices. The valve mechanism disclosed uses a complex arrangement of sliding valves and pressure actuated slide and ball check valves by which fluid continuously flows through the valve assembly from the source pressure to the exhaust until the lever is depressed in one position which simultaneously pressurizes one side of the cylinder and exhausts the other side of the cylinder. When the valve lever is lifted both the pressure to the cylinder and the exhaust to the cylinder are closed off such that the cylinder and piston retains its existing position. The raised handle returns the valve again to its neutral condition in which fluid circulates in tandem from the pressure source to the exhaust source. Moving the handle to its second index position and depressing it there actuates the cylinder and piston to pressurize and exhaust the opposite side so the piston removes in the opposite direction from the first index position. The '207 patent does not disclose a means for obtaining other operational neutral conditions such as completely closed, completely open, or floating cylinder and piston condition, but only discloses the tandem neutral arrangement.
Another poppet valve arrangement for automatic dispensing of soda water is disclosed in U.S. Pat. No. 868,322 which shows an arrangement of parallel reciprocation of four spring actuated valves axially aligned around the axis of a rotary actuation cam. The stems of the valves are adapted to be engaged by sliding inclined cam projections on the face of a rotary operating disc or plate. The springs serve to close those valves when the valve stems are not engaged by the cam projections. In the four valve arrangement disclosed, the projections are at diametrically opposed positions on the face of the rotary plate such that two opposed valves are opened simultaneously while the other two valves are simultaneously closed. The use of sliding inclined cams requires substantial rotational force when working with high pressure cylinder and piston machinery, as opposed to soda dispensing as in the '322 patent. Further there is no disclosure or suggestion in the '322 patent of a means by which the cylinder and piston arrangement can simultaneously receive pressurized fluid and discharge exhaust fluid. In particular, there is no suggestion of means for converting such a device to one which controls simultaneous flow of pressurized fluid to and from the working means and also one which is adaptable to provide any one of various operational neutral conditions including closed, open, float and tandem.
Generally the prior valves do not allow a construction which requires only outside metal turning, straight internal boring, outside milling, drilling and tapping. The prior devices do not provide for a control valve assembly which is economical, efficient and easily maintainable while providing complete control of pressurized fluid to and from a working cylinder and piston arrangement and which has easily changeable operating cams for selecting any one of four operational neutral conditions from among closed, open, float or tandem as may be required by a particular working environment.